Novel vinyl chloride resins and compositions incorporating such resins

ABSTRACT

Novel vinyl chloride copolymers including a hydroxyalkyl acrylate or methacrylate or allyl alcohol, an epoxy-containing vinyl monomer and an acid functionality from either certain carboxylic acid-containing monomers or a phosphorus ester moiety in selected proportions provide suitable binder resins for applications such as magnetic recording media, imparting desirable thermal stability together with enhanced dispersion and magnetic property characteristics and miscibility with elastomers employed in such media.

This application is a continuation of application Ser. No. 787,121 filedOct. 15, 1985, now abandoned.

RELATED APPLICATION

Colon and Mallon Ser. No. 636,895, filed Aug. 2, 1984, now abandoned,for Novel Phosphorylated Reaction Products and CompositionsIncorporating Such Products.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

This invention relates to novel vinyl chloride resins and, moreparticularly, to novel resins for use in compositions to be used inmagnet recording media, enhancing the dispersion and magnetic propertycharacteristics of such medium.

2. Description Of The Prior Art

Over the years, magnetic recording has come to occupy a vital place in amyriad of industries. Magnetic tape is accordingly utilized for audio,video, computer, instrumentation and other recordings. Magneticrecording media are utilized in a variety of forms, including, forexample, magnetic cards and disks, reels, video tapes, high performanceaudio tapes, computer tapes, floppy disks and the like.

While there are several different types of magnetic recording media, alltypes consist of a layer of magnetic particles, sometimes referred to as"pigment", coated on a plastic, paper or metal base. Information to berecorded is stored in the magnetic pigment applied to the base as aseries of small domains magnetized by a recording head. The coatinglayer of the magnetic pigment includes a binder system which provides acohesive matrix between the magnetic pigment particles and adheres suchparticles to the base.

The magnetic coating is applied to the base by coating equipment suchas, for example, a gravure roll coater, and the coated base thentypically immediately proceeds to a magnetic orientation step whereinorientation of the pigment particles is effected on the undried layer.In this step, the long axis of the pigment particles, typically acicularcrystals, is made to coincide with the magnetization direction.

In order to achieve good recording performance, the magnetic coatingmust possess a wide variety of characteristics. Pigment particles,desirably of relatively uniform particle size, should form as high aproportion of the coating layer as possible. Further, the degree ofdispersion of the pigment particles in the coating, often evaluated asdegree of gloss, should be as high as possible. Further, the highlydispersed pigment particles must be capable of being adequately orientedas previously described (the degree of orientation often measured as"squareness").

Still further, the adhesion and wear resistance of the magnetic coatingor film should be high. Also, the coefficient of friction of themagnetic surface should be low against the head material, and yet havean adequate value against the driving media such as pitch rollers andcapstan rollers.

Satisfying these and other diverse criteria have proven to require adelicate balance of basically reciprocal, or opposing, properties. Asubstantial amount of effort over the years has been directed toimproving the various characteristics of magnetic recording media.

To satisfy the performance criteria, the binder system must possessadequate modulus, yet have satisfactory tensile strength and resilience.It has generally been found desirable to satisfy these criteria byutilizing more than one material in the binder system. Typically, apolymer of relatively high molecular weight which is capable of beingcross-linked or cured is utilized to provide the desired modulus.Various elastomers are also incorporated to achieve the desiredresilience, toughness and durability.

Conventional binder systems include a wide variety of high Tg (viz. -glass transition temperature) hardening polymers or resins, such as, forexample, polyacrylates, polyesters, polyester amides, polyhydroxyethersand copolymers from monomers such as vinyl chloride, vinyl acetate,acrylonitrile, vinyl alcohol, vinyl butyral, and vinylidene chloride incombination with low Tg elastomeric polymers, including nitrile rubbers,polyesters, alkyd resins and polyester polyurethanes. The latterelastomers often represent the material of choice for high performanceapplications. Such resins have excellent toughness and abrasionresistance. Typically, the hardening polymers contain hydroxylfunctionality since crosslinking to further increase the modulus,durability and abrasion resistance characteristics can then be achievedby using polyfunctional isocyanates.

The degree of dispersion and the capability of the pigment particles tobe oriented in many binder systems are often considered inadequate inthe absence of dispersion aids. A wide variety of techniques have beenproposed to improve these characteristics. Thus, many surface activeagents have been employed for this purpose. These include higheraliphatic amines, higher fatty acids, phosphoric acid esters of higheralcohols such as polyoxyethylene phosphate alkyl ethers, esters ofhigher fatty acids and sorbitol, sodium alkylbenzenesulfonate,betaine-type, nonionic surface active agents and the like.

Magnetic coatings obtained by employing such surface active agentsgenerally exhibit uniform dispersion of magnetic powder as well as goodorientation, when the powder or pigment is in the form of acicularparticles. On the other hand, utilization of such agents often adverselyaffects wear resistance or causes difficulties in quality during use.These problems are often attributed to migration or blooming of suchsurface active agents to the magnetic coating surface or to unnecessaryplasticization of the hardening resin or of other components in themagnetic coating.

One attempt to obviate the migration problem is suggested by GreatBritain Patent No. 2,097,415A. This suggests using with a cross-linkableor polymerizable resin binder a phosphoric acid ester having at leastone polymerizable unsaturated double bond. Preferably, the phosphoricacid ester is a product obtained by reacting a phosphoric acid ester ofa compound having two or more hydroxyl groups with an acrylic ormethacrylic compound having a functional group reactive with anisocyanate group and also with a polyisocyanate compound. The phosphoricesters disclosed include two major types: (1) the reaction products of along chain alkylether or polyester, an acrylic or methacrylic compoundhaving a functional group reactive with an isocyanate group, and apolyisocyanate compound with (2) phosphoric esters of hydroxyalkylacrylates. Other binder systems disclosed utilize compounds containingvarious hydrophilic groups such as sulfates, sulphonates, hosphonatesand the like.

Japanese application No. 116,474 discloses a magnetic layer bindercomposition of a polyurethane and optionally a polyester containingsulphonate groups, and a vinyl chloride polymer containing sulphonate,sulphate, carboxylate or phosphonate groups. The binder is stated tohave good dispersing function to magnetic powder and the recordingmedium to have excellent service durability and good surface gloss.

Japanese Patent No. J57092421-A(8229) discloses a magnetic recordingmedium which includes a polyester urethane having (1) at least onehydrophilic group such as --SO₃ M,--OSO₃ H, --COOM, --P(O)(OM')₂, --NH₂,--NHR, NR₁ R₂, a bond NR₁ R₂ R₃, wherein M may be H, Li, Na or K; M' maybe H, Li, Na, K or a hydrocarbon group; and the R groups may behydrocarbon groups and (2) at least two acrylic type double bonds.

Japanese No. J57092422-A(8229) discloses a magnetic layer containing apolyurethane or polyester resin having (1) at least one hydrophilicgroup selected from --OSO₃ H, --COOM, --P(O)(PM')₂ wherein M may be H,Li, Na, K and M' may be H, Li, Na, K or a hydrocarbon group and (2) amolecular weight of 200 to 5000 per hydrophilic group.

International Publication No. W08400240-A discloses a magnetic recordingmedium containing a polyvinyl chloride-vinyl acetate-vinyl alcohol and apolyurethane resin containing polar groups such as --SO₃ M, --OSO₃ M',--COOM or ##STR1## wherein M may be H, Li, Na or K and M₁ and M₂ may beLi, Na, K or an alkyl group, preferably an alkyl group with up to 23carbon atoms.

Japanese J55117734-A(8043) discloses a binder for a magnetic recordingmedium which contains a copolymer of a phosphoric acid ester of analkylene glycol acrylate or an alkylene glycol methacrylate and acopolymerizable monomer. The wetting properties to ferromagneticmaterial is stated to be very good, so that dispersibility in the binderis improved. Blooming is said not to occur as no high aliphatic acid,metallic soap, or the like is used.

Among the binder polymers in use in magnetic coating media arecommercially available, partially hydrolyzed, (viz. - partly saponified)vinyl chloride - vinyl acetate coploymers and terpolymers.Unfortunately, the dispersion and orientation characteristics ofcoatings utilizing such binder polymers are typically less than isdesired. Considerable efforts have been undertaken to improve thesecharacteristics with the use of a wide variety of dispersion aids.

U.S. Pat. No. 4,420,537 to Hayama et al. thus discloses a magneticrecording medium including a commercially available vinyl chloride-vinylacetate-vinyl alcohol copolymer and a phosphoric ester type anionicsurfactant (e.g.--"GAFAC RE 610"). It is noted that when the content ofthe surfactant is more than 5 weight percent of the coating, thesurfactant is bloomed out from the magnetic layer.

U.S. Pat. No. 4,153,754 to Huisman notes difficulties with priordispersing agents. Low molecular weight agents, such as lecithin, havethe disadvantage that an excess is necessary to fully cover theparticles to be dispersed. The high molecular weight dispersing agents,as described, for example in Netherlands Patent Application No.65.11015, have the disadvantage that, due to their poor wettingproperties, agglomerates of the particles are also covered with adispersing agent. It is not readily possible, or it is possible only bythe use of much energy, to disintegrate such agglomerates to individualparticles. Huisman suggests using an Nacylsarcosine derivative as adispersing agent with the binders. The Examples show use of such adispersing agent with a commercially available vinyl chloride-vinylacetate-vinyl alcohol terpolymer.

U.S. Pat. No. 4,291,100 to Horigome et al. discloses a magneticrecording medium utilizing a polyoxyethylenesorbitane higher fatty acidester surfactant. The Examples include use of such surfactants withvinyl chloride-vinyl acetate copolymers and vinyl chloride-vinylacetate-vinyl alcohol terpolymers.

U S. Pat. No. 4,305,995 to Ota et al. shows a magnetic recording mediumincluding a mixture of sorbitan mono-, di- and tri- higher fatty acidester surfactants. The Examples show use of such surfactants with vinylchloride-vinyl acetate copolymers.

U.S. Pat. No. 4,330,600 to Kawasumi et al. discloses a magneticrecording medium in which the dispersion characteristics of magnetizableparticles are improved which results in improved saturation magneticflux density and squareness ratio. These are achieved by treating themagnetizable particles with a titanium alcoholate compound having atleast one group which is easily hydrolyzed and at least one oleophilicgroup which is hard to hydrolyze in an organic solvent. The examplesshow use of such titanium alcoholates with a commercially availablevinyl chloride-vinyl acetate copolymer binder.

U.S. Pat. No. 4,400,435 to Yoda et al. notes that vinyl chloride-vinylacetate copolymers have been used as binders, but that such copolymersdo not have functional groups whereby it is easy to improve thedispersibility of magnetic powder in a magnetic layer. It is furthersaid that it is not easy to carry out a thermosetting reaction. The useof vinyl chloride-vinyl acetate-vinyl alcohol copolymers instead hadbeen proposed; and, because of the hydroxyl groups present, thedispersibility of magnetic powder is improved and the thermosettablereaction can be performed. However, because of the vinyl alcoholcomponent, the glass transition temperature of the copolymer isdisadvantageously high so as to provide difficulties in improving thesurface properties by a calender process. A magnetic recording mediumhaving improved orientation and maximum residual magnetic flux densityis provided by using a vinyl chloride-vinyl acetate-maleic acidcopolymer having a content of the maleic acid component of at least 1.5percent.

In addition, there are available various vinyl chloride-vinyl acetateresins which are employed in magnetic recording media. For example, suchresins include vinyl chloride-vinyl acetate-vinyl alcoholmaleic acidpolymers in which the vinyl alcohol portion is obtained by hydrolysis.

J56077930-A(8133) discloses magnetic recording media in which asubstrate is coated with a magnetic lacquer composed of ferromagneticpowder bonded with a binder containing a copolymer of 70-95 weightpercent vinyl chloride and 1-25 weight percent hydroxyethylacrylate orhydroxyethylmethacrylate and 0-10 (meth)acrylic acid. It is stated thatthe squareness ratio and mass residual magnetic flux density areimproved. When polyisocyanate (hardening agent) is added, the abrasionresistance is also improved.

U.S. Pat. No. 4,415,630 to Kubota et al. discloses a radiation-sensitivemodified resin which is capable of being cross-linked by radiation. Asone example, thermoplastic resins which can be effectively modified forradiation sensitivity include vinyl chloride-based copolymers such asvinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinylchloride-vinyl acetate-maleic acid copolymers, and vinyl chloride-vinylacetate-end-OH-side-chain alkyl radical copolymers. Such thermoplasticresins which have one or more hydroxyl groups in the molecule can bereacted with a polyisocyanate compound, followed by reaction with amonomer having groups reactive to the isocyanate group and also havingunsaturated double bonds that harden upon irradiation at a rate of onemolecule of the former to one or more molecules of the latter. A furtherexample involves a reaction product of the compound having at least oneepoxy group in the molecule and a monomer having groups reactive withthe epoxy group and also having radiation-setting, unsaturated doublebonds. Specifically, an epoxy-containing thermoplastic resin, obtainedby radical polymerization with glycidyl alcohol, is reacted with acrylicacid. By the ring-opening reaction of the carboxyl and epoxy groups, aresin is obtained which carries the acrylic double bonds as a pendantgroup.

Further, U.S. Pat. No. 3,755,271 to Montgomery discloses terpolymers ofvinyl chloride, vinyl acetate and certain acrylic esters. Theseterpolymers can be employed alone or in admixture with other resins tomake useful coatings. U.S. Pat. No. 3,884,887 to Montgomery provides asimilar disclosure.

Also, East German DL140-463 discloses a crosslinkable binder forproviding improved weather resistance, particularly to water, forvarious substrates. The composition comprises an acrylate ester, vinylchloride, maleic acid or the half ester and one of the following: anepoxy containing monomer or (2) hydroxyethylacrylate or (3) a derivativeof methylacrylamide.

Japanese Publication No. JA7203734-R discloses a composition which issaid to provide good weathering properties and chemical resistance. Thecomposition includes 2-6 weight percent of acrylic acid or maleic acid,3-15 weight percent of glycidyl methacrylate and hydroxyethylacrylate,and 79-95 weight percent of an acrylate ester, alone or with otherolefinically unsaturated monomers such as styrene or vinyl chloride.

Co-pending application Ser. No. 636,895 now abandoned, discloses novelphosphorylated compositions of a vinyl chloride copolymer or terpolymerhaving improved dispersion characteristics which are suitable for use inapplications such as magnetic recording media. While such phosphorylatedcompositions provide improved dispersion characteristics, there stillremains the need for improvement. More specifically, the phosphorylationreaction is not as facile as would be desired. Moreover, it is necessaryto carefully carry out such reaction because of the inherent lack ofthermal stability of such vinyl chloride compositions.

In addition, while vinyl chloride compositions are highly desirable foruse as binder resins in magnetic recording media, it has long beenrecognized that compositions having improved thermal stability would behighly desirable. This is apparent because a wide variety of conditionsmust be met. Thus, binder resins must be storage stable under ambientconditions as well as being stable during a variety of processingoperations in forming the various products, including grinding, dryingand calendering operations. Likewise, the product must not undulydegrade in storage and must provide substantial durability in operation.

From the product performance standpoint, a high level of stability isdesirable for such binder resins so that the magnetic recording mediumperforms adequately during its expected lifetime. The primary binderfunction of holding the particulate magnetic pigment on the base filmthrough the rigors of production and use are critically dependent uponthe molecular weight of such resins. Cumulative exposure to highertemperatures can reduce the molecular weight of vinyl resins, whichresults in premature mechanical failure. The obvious flaking of pigmentand loss of information can be, of course, catastrophic. Degradationoften manifests itself by low molecular weight products blooming to thesurface with fouling of the heads or tape sticking to the guides.

Another failure mode results from the failure of the other components inthe system due to the evolution of HCl from vinyl chloride resins. Thus,the polyester urethane elastomer binder ingredient often used in suchmedia can itself degrade through acid-catalyzed hydrolysis. The loss ofmolecular weight and evolution of blooming species can cause the sameproblem as the primary degradation in the hardening polymer. In theextreme case, low levels of HCl could well be generated duringlong-term, still-frame playing which could corrode the head surfaces.

Accordingly, despite the considerable prior effort in this field, theneed remains for binder systems utilizing vinyl chloride resins that cannot only achieve the desired dispersion and magnetic characteristicsover a widespread variety of usage requirements but can also providerelative freedom from thermal instability problems.

OBJECTS OF THE INVENTION

A principal object of the present invention is to provide novel vinylchloride polymers for use in applications such as magnetic coatings toimpart desirable dispersion and orientation characteristics while havingsuperior thermal stability.

A further object of this invention provides a novel binder system for amagnetic recording medium which may be substituted for conventionalbinders in formulations as essentially a plug-in substitution.

Yet another object lies in the provision of novel compositions that maybe obtained by utilizing a straightforward, facile synthesis. A relatedand more specific object provides binder compositions that may be formedin a one-step, or direct, polymerization.

Another object of the present invention is to provide a binder systemfor magnetic recording media which minimizes or eliminates the need toemploy a dispersing agent which ca cause blooming in use.

A still further object lies in the provision of a magnetic coating whichis capable of being processed in conventionally utilized magneticcoating equipment.

These and other objects of the present invention will be apparent fromthe description set forth hereinafter.

SUMMARY OF THE INVENTION

The present invention is based on the a binder system for particulatematter to be used in magnetic recording media, which is capable ofimparting not only desirable dispersion and magnetic characteristics butalso excellent thermal stability, and is provided by utilizing acopolymer of vinyl chloride, a hydroxyalkyl acrylate or methacrylate orallyl alcohol, an epoxy-containing vinyl monomer, and a monomer havingan organic carboxylic acid moiety selected from the group consisting ofacrylic acid, methacrylic acid, maleic acid or anhydride, itaconic acidand fumaric acid or a phosphorus ester moiety. Optionally, the bindersystem can include minor amounts of a vinyl ester such as vinyl acetate.

The relative amounts of the various constituents of the binder resins ofthis invention must be carefully tailored to provide the desiredcomposite properties. Thus, the relative amount of vinyl chloride shouldbe adequate to provide the desired mechanical characteristics, asdetermined by the Tg (viz.--glass transition temperature) for the resin.The hydroxyalkyl acrylate or methacrylate or allyl alcohol should bepresent in the media, in an amount to provide facile curing withpolyisocyanates and miscibility with the elastomer component, when thiscomponent is used. The acid functionality (either a carboxylic orphosphoric acid) should be utilized in an amount that will provide thedesired dispersibility characteristics but not in excess sinceundesirable rheological characteristics or the like can result. Theepoxy-containing moiety is present in an amount necessary to provide thedesired thermal stability as well as, when a phosphorylating agent isused, to provide reactive groups to incorporate adequate amounts of thephosphoric acid functionality. Vinyl esters such as vinyl acetate may beused in minor amounts, commonly being incorporated in the preparation ofvinyl chloride polymers to impart processing latitude.

In accordance with one aspect of the present invention, when a monomercontaining a carboxylic group is used to provide the acid functionality,it has been found that the binder resins can be prepared by a one-step,or direct, polymerization. This affords a facile preparation that canallow considerable economic savings. Thus, it is considered that anypost modification following preparation of a polymer can add at least50% to the manufacturing cost.

DETAILED DESCRIPTION OF THE INVENTION Resin Composition

With respect to the vinyl chloride constituent, this will generally bethe major component that determines the adequacy of the mechanicalproperties necessary to appropriately function as a binder resin inmagnetic recording media and the like. Accordingly, it is necessary toutilize an amount of vinyl chloride sufficient to provide the requisiteproperties for the resin, which properties can be adequately determinedby reference to the Tg of the resin.

It will be generally desired to utilize amounts of vinyl chlorideadequate to provide the resins of this invention with a Tg of at least40° C., preferably at least about 50° C., and more preferably at leastabout 70° C. It will accordingly be necessary to utilize a resin havingat least about 70% by weight of vinyl chloride. More preferably, it isdesirable to utilize about 80 to about 90% by weight of vinyl chloride.Amounts in excess of about 90% by weight may have inadequate solubilityin conventional solvents.

Concerning the hydroxyalkyl acrylate and methacrylate or allyl alcoholconstituent, an amount should be present in the resin that is sufficientto provide the requisite cross-linking upon reaction with thepolyisocyanate employed and, when used, miscibility with the elastomer.It is preferred to utilize an amount which will provide at least about0.5% by weight of hydroxyl groups to achieve this result. As an upperlimit, since these constituents will typically have a Tg substantiallyless than that of vinyl chloride, it is accordingly desirable to utilizean amount which provides no more than about 2.5% by weight of hydroxylgroups, although amounts providing up to about 3% hydroxyl groups may beemployed in some applications. In this connection, relative to thehydroxyalkyl acrylates, somewhat higher amounts of the hydroxyalkylmethacrylates may be employed since the Tg of such monomers willgenerally be somewhat higher.

Among the hydroxyalkyl acrylates and methacrylates, it is preferred toutilize from the economic standpoint either hydroxypropyl acrylate orhydroxyethyl acrylate. While less advantageous from the economicstandpoint, other species that may desirably be utilized includehydroxyethyl methacrylate and hydroxypropyl methacrylate and allylalcohol. The methacrylates have the advantage from the performancestandpoint of having a higher Tg than that of the acrylates.

As regards the component imparting the requisite dispersibility, whetherphosphorylation is involved or whether dispersibility is provided with amonomer yielding or having a carboxyl group, an amount should be used asa minimum which will impart the requisite dispersibility. Where amonomer having a carboxyl functionality is used, this will generallyrequire at least 0.2% by weight of the carboxyl groups, preferably atleast about 0.5%. Where the acid functionality is obtained byphosphorylation, the resin should contain at least about 0.03% by weightphosphorus.

It has been found that an excess acid functionality can lead toundesirable rheological effects. Such effects are apparent due toundesirably high viscosities which result. Accordingly, it is generallypreferred to avoid amounts in excess of about 1.5% by weight, morepreferably about 1.0% by weight of carboxyl groups. When the acidfunctionality is provided by phosphorylation, it is preferred to avoidamounts that result in greater than about 1.0% by weight of phosphorusin the resin. More preferably, the phosphorus content is maintained inthe range of 0.03 to about 0.5% by weight.

Among the organic carboxylic acids which are useful are acrylic,methacrylic, maleic , itaconic, fumaric, and the like. Of course,anhydrides such as maleic anhydride can likewise be employed in thesynthesis of the resins.

With respect to the constituent imparting thermal stability, a compoundproviding a source of oxirane oxygen is utilized. Epoxy-containing vinylmonomers such as acrylic or methacrylic esters may thus be employed.More specifically, glycidyl acrylates and methacrylates are useful, asis 4-vinyl cyclohexene monoepoxide (sometimes referred to as"vinylcyclohexene monoxide"). Other species that should be capable ofbeing employed include methyl glycidyl methacrylate, methyl glycidylacrylate, allyl glycidyl ether, the allyl glycidyl ether of bisphenol-A,allyl phenol glycidyl ether, glycidyl butadiene, and the like.

The amount of the epoxy-containing vinyl monomer should be that whichprovides the resin with the desired heat stability. Relatively highermolecular weight resins tend to be relatively more stable than lowermolecular weight vinyl chloride copolymers. Accordingly, the amountutilized will be determined, in part, by the molecular weight of theresin being prepared. Typically, an amount that provides from about 0.1to 1.5 percent oxirane oxygen should be useful. This will correspond,for example, to about 1 to about 12 percent by weight of glycidylmethacrylate.

One major consideration in the amount utilized is the Tg of the resinitself since most useful constituents will reduce the Tg of the resin.Further, when phosphorylation is utilized to provide the acidfunctionality, it is necessary to incorporate an adequate amount of theoxirane oxygen source to not only provide the requisite thermalstability but also to afford adequate functionality to incorporate thedesired amount of phosphate.

Optionally, and if desired, a vinyl ester such as vinyl acetate may beemployed. Other useful vinyl esters include vinyl formate, vinylpropionate, vinyl butyrate and the like. Other higher vinyl esters up toabout 6 carbon atoms also may be used, if desired. Typically, such vinylesters are employed in preparing vinyl chloride copolymers andterpolymers so as to allow what is considered to be improved processinglatitude. Suitable amounts can vary up to about 12% by weight of theresin.

Preparation of the Resin

Conventional solution polymerization techniques may be desirablyutilized, as will be discussed hereinafter, to form the binder resins ofthis invention. Similarly, other polymerization techniques such asconventional suspension or emulsion polymerization may also be used.Thus, the process employed for making the resins of this invention isnot critical, and such technology is well understood by those in theart. Suitable preparative techniques are, for example, set forth in U.S.Pat. No. 3,755,271.

In general, and as an illustrative example, the resins of this inventionmay be prepared by utilizing solution polymerization, employing asolvent for the resulting resin as well as for the various componentsemployed. Suitable solvents include, for example, the conventional estersolvents such as butyl acetate, ethyl acetate, isopropyl acetate, andthe like, as well as the ketone solvents such as methylethylketone,methyl-n-butylketone, methylisopropylketone, and the like.

The polymerization may be carried out either batch-wise or continuously.Typically, the ratio of solvent/monomer will vary from about 0.3/1 toabout 4/1, depending upon the molecular weight desired. The temperatureselected may vary from about 35° C. to about 80° C., depending upon thereaction rate and resin molecular weight desired. Any oil-soluble, freeradical catalyst may be used in an amount varying from about 0.01 toabout 3.0%, based on the weight of the monomer. Suitable catalystsinclude, as illustrative examples, dibenzoyl peroxide, dilauroylperoxide, azobisbutyronitrile and isopropyl peroxide carbonate. Anypressure above the vapor pressure of the components of the system may beemployed, pressures from about 30 to 100 psi being typical.

In accordance with one aspect of this invention, when the requisite acidfunctionality is provided by employing an organic carboxylic acidmonomer, the resins of the present invention may be prepared in adirect, one-step polymerization. Surprisingly, it has been found thatthe resin preparation may be carried out without any significantby-product reactions taking place, such as might be expected to occurbetween the organic carboxylic acid and the epoxy monomer used. Indeed,these resins may be prepared using the equipment and reaction parametersemployed in making commercially available vinyl chloride-vinyl acetatecopolymers and the like.

When the acid functionality is provided through phosphorylation, theresins of the present invention will typically be prepared in a two-steppolymerization. The first step involves forming an intermediate from allof the monomer components other than the phosphorylating agent. This canbe prepared using the techniques and parameters described in the directpolymerization, one-step process.

Thereafter, the phosphorylation reaction may be carried out bydissolving the intermediate in an aprotic solvent such as, for example,methylethylketone, tetrahydrofuran or cyclohexanone, to which thedesired phosphorylating agent is added with stirring. The reaction mayproceed at room temperature or, if desired, elevated temperatures, againwith stirring, until the reaction is complete.

The temperature at which the phosphorylating reaction is carried out isnot critical but is dependent on the phosphorylating agent employed. Ingeneral, however, it is desirable that the phosphorylation reaction becarried out at elevated temperatures to provide adequate reaction of theoxirane groups with the phosphorylating agent and insure completereaction, suitable temperatures being from about ambient to about 60° C.While the resins of the present invention are characterized by superiorthermal stability, it will be generally preferable to keep thetemperature as low as possible, consistent with the conditions needed toinsure adequate reaction. Since heat may be generated, such as when highspeed agitation equipment is used, it may be desirable to utilizecooling means to minimize the temperature rise. Minimizing the thermalhistory during resin preparation should translate to enhanced thermalstability of the resin during use.

In carrying out the phosphorylation, the reaction should utilize aphosphorylating agent and conditions that will avoid forming significantamounts of higher molecular weight species, as would result when twointermediate molecules are linked together through the phosphate moiety.The presence of such high molecular weight species can result in systemshaving undesirably high viscosities. This is obviously of greatersignificance when the intermediate starting material is already of arelatively high molecular weight.

Suitable phosphorylation agents include phosphoryl chloride and itsderivatives: PO(OR²)_(n') Cl_(3-n'), wherein n' is 0, 1, 2, or 3 and R²is hydrogen, a saturated or unsaturated hydrocarbon radical having from1 to about 20 carbon atoms, a cycloalkyl radical of from 1 to about 20carbon atoms, an alkyl acrylate or methacrylate in which the alkylradical is from 1 to about 10 carbon atoms, aryl and substituted aryl offrom 6 to about 20 carbon atoms and adducts of hydroxyalkyl acrylatesand methacrylates and a lactone, and mixtures thereof, or phosphoruspentoxide or the reaction production of phosphorus pentoxide with ahydroxylcontaining material, including water, saturated or unsaturatedalcohols having from 1 to 20 carbon atoms, hydroxyalkyl acrylates ormethacrylates having from 2 to 10 carbon atoms, substituted andunsubstituted phenols and adducts of hydroxyalkyl acrylates andmethacrylates and a lactone, and mixtures thereof. Suitable adducts ofhydroxyalkyl acrylates and methacrylates and a lactone are described inthe copending Colon et al. application, Ser. No. 636,895, now abandonedthe disclosure of which is herein incorporated by reference.

The phosphorylation reaction may be carried out in any of a variety ofaprotic solvents. Suitable examples include methylethylketone,tetrahydrofuran and cyclohexanone. The amount of the intermediatestarting material added to the aprotic solvent may be varied within awide range, provided the material is soluble in the solvent and theviscosity of the solution is not so high as to prevent stirring. Ingeneral, a level of about 25 weight percent has been satisfactorilyemployed. The relative amounts of the phosphorylating agent and theintermediate may be selected to provide the desired level ofphosphorylation.

Inclusion of small amounts of water in the reaction mixture shouldprevent the formation of the undesirable high molecular weight species.Often, the intermediate will contain a small amount of water that issufficient to prevent the formation. However, if the water level isunduly high, this will result in an inefficient utilization of thephosphorylating agent. As an alternative, the intermediate may be dried;and the level of water optimized to maximize the utilization of thephosphorylating agent while still preventing the formation ofsignificant amounts of the high molecular weight species.

The level or degree of phosphorylation suitable to provide the desiredcharacteristics will be generally such that, based on the weight of thephosphorylated intermediate, the phosphorus content of the material maybe as low as about 0.03% by weight, more desirably at least about 0.1%.However, levels above about 1.0% by weight should be avoided so as toprevent undesirable resin rheology and the like which will adverselyaffect the desired characteristics.

It has been found that the efficiency of the phosphorylating reaction isimproved relative to that which can be obtained by reaction with thehydroxyl groups in a vinyl chloride-vinyl acetate-vinyl alcoholterpolymer or the like. More specifically, in contrast to the 10 to 20percent efficiency obtained when utilizing hydroxy groups, the presentinvention is capable of achieving efficiency on the order of about 40 toabout 50 percent. This is achieved due to the epoxy functionalityinvolved in the phosphorylation. Indeed, this reaction is sufficientlymore facile so that essentially no reaction occurs with the hydroxylgroups present in the resins of this invention.

Alternatively, if desired, certain other preparative techniques may befeasible. For example, to avoid a second step in the reaction, an adductmay be formed by reaction of the desired phosphorylating reagent withthe oxirane oxygen source, e.g. glycidyl methacrylate. This adduct maythen be utilized in forming the resins of this invention in a directpolymerization.

Also, the intermediate resin reaction product in the solvent used may bedirectly reacted with the desired phosphorylating agent without firstrecovering the intermediate. After completion of the phosphorylatingreaction, the resulting resin can then be recovered by conventionaltechniques.

DESCRIPTION OF THE PHOSPHORYLATED PRODUCTS

It can be seen from the description of the phosphorylating agentsdescribed above that phosphorus may be included in the phosphorylatedvinyl resins of the present invention in the form of a wide variety ofphosphorus ester moieties, characterized by the formula: ##STR2##wherein R⁶ comprises hydrogen, an alkyl or alkenyl radical having from 1to 20 carbon atoms, an alkyl acrylate or methacrylate residue havingfrom 2 to 10 carbon atoms in the alkyl segment, substituted andunsubstituted phenyl, the lactone-adducts referred to herein, ormixtures thereof.

The formula for the phosphorus moieties represents an idealized formula.Depending upon the reaction conditions and the particularphosphorylating agent employed, the resulting reaction product comprisesa distribution of mono-, di- and tri-phosphate esters. Accordingly, inthe idealized formula, R⁶ may be solely hydrogen (providing a phosphatemonoester), a mixture of hydrogen and the hydrocarbon residue of thehydrocarbon from which the derivative was prepared (providing adiester), or solely the hydrocarbon residue (providing a triester). Forthe purpose of the present invention, the phosphorus moiety will bedescribed in terms of the formula set forth, wherein the formula is usedto represent the reaction product, including those situations wherein acomplex mixture or distribution of compositions is obtained.

MAGNETIC RECORDING MEDIUM

Base

Any base or substrate may be utilized, and the particular substrate ofchoice will be dictated for the most part by the particular application.Polyethylene terephthalate and polypropylene films are in wide use asbase materials for magnetic recording media. Where heat resistance is animportant consideration, a polyimide film, polyamide film, polyaryletherfilm, or the like may be utilized. In the case of a polyester film as athin base, it is often used after monoaxial or biaxial orientation. Itis likewise well known that pretreatment of the film may be beneficialto promote wetting and adhesion.

COMPOSITION OF THE MAGNETIC COATING LAYER

The magnetic particles may be any of those known and useful inconventional magnetic recording media. Representative examples includeacicular or granular γFe₂ O₃, Fe₃ O₄, Co-doped γ-Fe₂ O₃, Co-doped γFe₂O₃ -Fe₃ O₄ solid solution, Co-base-compoundadsorbed adsorbed γFe₂ O₃, aCo-base-compound-adsorbed Fe₃ O₄ (including those oxidized to anintermediate state between itself and γ-Fe₂ O₃), and acicular CrO₂. (Theterm "Co-base compound" as used herein means cobalt oxide, cobalthydroxide, cobalt ferrite, cobalt ionadsorbates and the like whichenable the magnetic particles to take advantage of the magneticanisotropy of cobalt in improving its coercive force). Also, themagnetic particles may be a ferromagnetic metal element or alloy, suchas Co, Fe--Co, Fe--Co--Ni, or the like. Such a fine magnetic particle isprepared in a number of ways, including wet reduction of the startingmaterial with a reducing agent such as NaBH₄, a treatment of the ironoxide surface with a Si compound and subsequent dry reduction with H₂gas or the like, and vacuum evaporation in a low-pressure argon gasstream. Fine particles of monocrystalline barium ferrite may be employedas well. The fine magnetic powder is used in the form of acicular orgranular particles, depending on the application of the resultingmagnetic recording medium.

It will be generally desirable to utilize a relatively large amount ofmagnetic particles in the coating layer. Typical compositions of thecoating layer will thus include about 65 or 70 to about 85 or 90 percentmagnetic particles, based upon the total weight of the coating layer. Asis known, it is desirable to utilize pigment particles of relativelyuniform size, with typically used particles having a long axis of about0.4 micron or even less being employed.

The remainder of the coating layer will comprise the binder system,including the hardening resin, and typically an elastomeric polymer, adispersant, a crosslinker and any auxiliary agents. Depending upon theresin of the present invention which is utilized, the dispersant as suchmay be minimized or even eliminated.

Conceptually, however, in addition to the pigment particles, the onlyadditional essential component in accordance with this invention is thehardening resin itself and the crosslinker. Typical coating layers will,however, often include the additional components identified dependingupon the particular end use application. As is apparent from the amountutilized in typical formulations of the pigment particles, the remainderof the coating layer will generally represent about 10 or 15 to 30 or 35percent by weight of the coating layer.

As has been previously discussed, the binder system will generallydesirably include an elastomeric polymer in an amount sufficient toprovide the coating layer with the desired resilience and the like. Manyelastomeric polymers suitable for this purpose are known and may beutilized. Polyester urethanes are often preferred for high performanceapplications. Suitable materials are commercially available. Thesematerials may be, in general, described as the reaction products ofpolyester polyols, short chain diols, and isocyanates. These resins haveexcellent toughness and abrasion resistance characteristics.

A wide variety of polyisocyanate crosslinkers are known and may be used.Typically, polymeric polyisocyanates are employed. As one example, it issuitable to use polymeric toluene diisocyanate (TDI) adducts. The amountof the crosslinking agent used is typically about 20 to 50 percent ofthe amount that would be required based upon the hydroxyl stoichiometry,although up to 100% of the stoichiometry may be employed, if desired.

As is known, a variety of auxiliary agents are sometimes employed in themagnetic coating layer. Such additives are known and may be employed, ifdesired for the particular application. Examples of such auxiliaryagents include antistatic agents, lubricants, sensitizers, levelingagents, wearresisting agents, and film-reinforcing agents.

In accordance with the present invention, the magnetic coating layerutilizes the resins of the present invention to provide the necessarydispersing and orientation characteristics of the coating, and tofunction as the hardening resin as well. No other hardening resin needbe employed; however, if desired, the resins of the present inventioncan be utilized with compatible hardening resins to provide the desiredmagnetic coating layer.

In accordance with this invention, the use of the resins of the presentinvention should provide improved dispersion and orientationcharacteristics. However, if desired, other conventional dispersingagents may be employed.

PREPARATION OF COATING

The recording medium may generally be prepared by dissolving the bindersystem in a sufficiently volatile vehicle to provide a coatabledispersion of fine magnetizable particles. The dispersion can then becoated onto the substrate to provide a coating thereon. The magneticrecording medium may be prepared by methods described in the art such asin, for example, S. Tochihara, "Magnetic Coatings and Their Applicationsin Japan", Progress in Organic Coatings, 10 (1982), pages 195 to 204.

Other Applications

While use of the resins of the present invention provides highlyadvantageous properties in magnetic recording media and the presentinvention has been described in conjunction with this application, itshould be appreciated that such materials likewise can be utilized asdispersants and/or hardening resins in any other application where thecharacteristics of such resins could desirably be incorporated. Forexample, conventional zinc-rich coatings are useful in many applicationswhich require corrosion resistance and the like. Such compositionstypically comprise a high percentage of zinc particles (up to 85 to 90percent by weight of the composition) and a resin together with suchoptional components as anti-settling agents, thickening agents and waterscavengers, as is known For zinc-rich maintenance coatings, and otherclear and pigmented coatings, any of the resins of the present inventionshould provide improved dispersibility and thus improved adhesion tosubstrates. The resins of this invention can accordingly be readilyutilized in conjunction with such coatings.

EXAMPLES

The following Examples are representative of the present invention, andnot in limitation thereof. The starting materials used, abbreviationsemployed, control resins evaluated, polymerization method used, thepreparation of the magnetic media formulations, and the evaluationtechniques utilized in the ensuing Examples were as follows:

STARTING MATERIALS AND CONTROL RESINS

Elastomer A

B.F. Goodrich "Estane® 5701 F-1" polyester polyurethane elastomer havinga specific gravity of 1.21, a Tg of -25° C. and a Brookfield viscosityof 300 cps. for a 15% total solids solution in tetrahydrofuran.

Resin A

A commercially available vinyl chloride-vinyl acetate-vinyl alcoholterpolymer having a composition of 90/4/6, respectively, and anintrinsic viscosity of 0.53.

Resin B

A commercially available vinyl chloride copolymer containing vinylacetate, vinyl alcohol and maleic acid and having a composition of90/4/5/1, respectively, and an intrinsic viscosity of 0.50.

ABBREVIATIONS USED

The following abbreviations are used in the following Examples:

VCl--vinyl chloride

VAc--vinyl acetate

GMA--glycidyl methacrylate

HPA--hydroxypropyl acrylate

AA--acrylic acid

SR--squareness ratio

SFD--switching field distribution

Hc--coercivity

Polymerization Procedure

Vinyl Copolymer

The vinyl chloride copolymers were produced via continuous solutionpolymerization in a stainless steel stirred tank reactor. Vinyl chlorideand the other monomers used, as well as the solvent, were pre-mixed andfed continuously to the reactor. The free radical initiator,diisopropyl/peroxydicarbonate, was also fed continuously as an acetonesolution, at a rate necessary to maintain constant conversion. Productsolution was continuously withdrawn from the reactor. The temperature inthe reactor was maintained at 50°-60° C. while the pressure was keptbetween 90-110 psi.

The product solution was stripped of unreacted vinyl chloride monomer.The polymer was then recovered from solution by precipitation with anisopropanol/water mixture, filtered, and dried in a fluid bed drier.

PHOSPHORYLATION PROCEDURE

A solution of the epoxy-containing vinyl chloride copolymer intermediatein an aprotic solvent was prepared. This solution was placed in astirred reactor and, to this stirred solution, was added the appropriateamount of the phosphorylating agent (either P₂ O₅ or polyphosphoricacid). This reaction mixture was then reacted at an initial temperaturebetween ambient and 60° C. for a period of from several minutes toseveral hours, depending upon the stirring rate. Since, in mostinstances, high speed agitation equipment was used, the final reactiontemperature was above the initial temperature. No cooling means wereused.

PREPARATION OF THE MAGNETIC MEDIA FORMULATIONS

Formulations were prepared by premixing 134 grams of a 15 percentcyclohexanone solution of the resin with 160 grams of cyclohexanone andadding 200 grams of cobalt-modified, iron oxide magnetic pigment withparticles having a long axis of about 0.4 micron ("PFERRICO 2566"magnetic pigment, Pfizer, Inc.). After the mixture was well blended withan air stirrer for 15-30 minutes, the resulting slurry was added to aPremier Mill filled with l.3mm. glass beads and milled for about onehour.

Those formulations containing only the resins of the present inventionwere discharged at this point and evaluated. Where Elastomer A was addedto the formulation, 134 grams of a 15% solution in cyclohexanone wereused. The formulation was then milled for an additional hour anddischarged.

MAGNETIC MEDIA EVALUATIONS

Gloss

This was evaluated by preparing a 1 mil drawdown on glass, allowing theformulation to air dry and then measuring the gloss with a 60° glossmeter.

Squareness

This was measured by preparing a 3 mil wet drawdown on a Mylar substrateand then pulling the Mylar across a bar magnet to orient the magneticparticles. Squareness was then measured on a 2X2 inch piece of thisoriented coating using a LDJ Model 7000A B-H Meter. According to thepigment manufacturer, the maximum squareness achievable with themagnetic pigment utilized is 0.84.

Switching Field Distribution (SFD)

This was obtained using the sample employed in determining squarenessand is a measure of the variation in particle coercivities. The lowerthe value, the more well defined is the recording zone. A value of lessthan 0.60 is considered desirable.

Coercivity (Hc)

Obtained using the squareness ratio sample, this measures themagnetizing field needed to reduce maximum magnetic induction to zero. Avalue of greater than 700 is considered desirable for the magneticparticle utilized.

Tensile Strength and Elongation

These values were obtained using ASTM-638 Type 5.

Viscosity

The values reported are Brookfield viscosities at 25° C., using RFSpindle #4 at 20 r.p.m.

Intrinsic Viscosity

The values reported employed the procedure set forth in ASTM D-1243,using cyclohexanone as the solvent.

EXAMPLE 1

This Example illustrates the compatibility of a thermally stable vinylresin containing hydroxyl functionality with Elastomer A.

A VCl/VAc/GMA resin having the composition 81/11/8 was prepared and wasthen hydrolyzed. The hydrolyzed resin was then phosphorylated using P₂O₅ and a resin/P₂ O₅ ratio of 500/1. The resulting resin had aphosphorus content of 0.20%, an intrinsic viscosity of 0.32 and a Tg of73° C.

The Tg of resin/Elastomer blends of 60/40 and 75/25 were, respectively,40° C. and 53° C. Since a single Tg was obtained for each blend and thevalue was between that of the resin and that of Elastomer A, the resinand Elastomer A were miscible and, accordingly, compatible. Accordingly,while not a resin of this invention, this Example illustrates thatmiscibility with elastomers can be obtained with vinyl chloride resinshaving hydroxyl functionality and that miscibility will vary withhydroxyl content.

EXAMPLES 2-7

These Examples show the phosphorylation of vinyl resins including asource of oxirane oxygen.

A VCl/VAc/GMA resin was prepared having the composition of 81/11/8.Resin samples were then phosphorylated in Examples 2-4 by mixing withthe phosphorylating agent at ambient temperature and then leftovernight. In Examples 5-7, the resins were phosphorylated by heating toreflux for 3 hours and were then cooled. Each sample was then coagulatedusing isopropanol/water (60/40), filtered, washed and dried (at about43° C. in vacuo) until a stable weight was obtained.

The relative amounts of the constituents and the percent phosphorus inthe phosphorylated product are set forth in Table I:

                  TABLE I                                                         ______________________________________                                                   Examples                                                           Constituent  2      3       4    5    6     7                                 ______________________________________                                        Resin        100    100     100  100  100   100                               Methylethylketone                                                                          100    100     100  100  100   100                               Polyphosphoric Acid                                                                         1      2      --    1    2    --                                P.sub.2 O.sub.5                                                                            --     --       1   --   --     1                                % Phosphorus 0.52   0.43    0.50 0.43 0.58  0.42                              ______________________________________                                    

These Examples show that both techniques produced essentially the sameproduct, efficiently incorporating the phosphate moiety into the vinylresin. While not resins of this invention since no hydroxylfunctionality is present and the resins would not be miscible withstandard elastomers used in magnetic recording media formulations, theseExamples do illustrate the more facile nature of the phosphorylationreaction with the epoxy groups in comparison to that when hydroxylfunctional resins are used. This can be seen from the level ofphosphorus that is incorporated which is significantly greater than canbe easily incorporated when employing hydroxyl functional resins.

EXAMPLES 8-9

These Examples show the magnetic properties of magnetic recording mediamade using the vinyl resins of this invention where the acidfunctionality is obtained using phosphorylation.

A resin was prepared using VCl/HPA/GMA/VAc to provide a composition,respectively, of 75/10/5.5/9.5. These samples had a Tg of 72° C., atensile strength of 5,400 and an elongation of 5.7% and an intrinsicviscosity of about 0.36.

The resin was phosphorylated in cyclohexanone, using a resin/P₂ O₅ ratioof 34/1 in Example 8 and 260/1 in Example 9 and an initial temperatureof 25° C. The reaction proceeded for 25 minutes in Example 8, reaching afinal temperature of 50° C. and proceeded for 20 minutes in Example 9,the ending temperature being 40° C. The resulting resin was recovered,and a magnetic recording media composition prepared.

Table II sets forth the viscosity and magnetic properties:

                  TABLE II                                                        ______________________________________                                                        Examples                                                      Property          8       9                                                   ______________________________________                                        60° Gloss  100     100                                                 SR                0.814   0.843                                               SFD               0.563   0.519                                               Hc                755     775                                                 Viscosity, cps.   5800    3500                                                ______________________________________                                    

Although the molecular weight of the resin is less than desirable, theseExamples demonstrate that excellent magnetic properties can be obtainedusing the phosphorylated resins of the present invention. In addition,these vinyl chloride copolymers are miscible with elastomers commonlyused in magnetic media formulations.

EXAMPLES 10-12

These Examples illustrate the magnetic properties of recording mediamade using the phosphorylated resins of this invention made with a resinhaving a higher intrinsic viscosity than that used in Examples 8 and 9.

Resins were prepared having the following compositions and physicalproperties:

                  TABLE III                                                       ______________________________________                                                    Examples                                                                      10       11      12                                               ______________________________________                                        Composition                                                                   VCl           72         74      74                                           HPA           13         12      12                                           GMA            7          7       7                                           VAc            8          7       7                                           Physical Properties                                                           Tg, °C.                                                                              72         71      71                                           Tensile Strength, psi                                                                       8000       6600    6600                                         Elongation, % 4.5        3.6     3.6                                          Intrinsic Viscosity                                                                         0.56       0.50    0.50                                         ______________________________________                                    

These resins were phosphorylated by reaction with P₂ O₅ in cyclohexanoneusing resin/P₂ O₅ ratios of 260/1 (Example 10), 180/1 (Example 11) and80/1 (Example 12). The initial temperature in Example 10 was 49° C., thereaction proceeded for 23 minutes, and the final temperature was 85° C.The respective reaction conditions for Example 11 were 50° C., 25minutes and 113° C., while the respective conditions for Example 12 were29° C., 10 minutes and 70° C.

Magnetic recording media were prepared using these resins, and themagnetic properties and viscosity are set forth below:

                  TABLE IV                                                        ______________________________________                                                Examples                                                              Property  10            11      12                                            ______________________________________                                        60° Gloss                                                                         86            85      80                                           SR        0.80          0.80    0.78                                          SFD       0.60          0.60    0.62                                          Hc        741           748     734                                           Viscosity 17,000        15,500  31,000                                        ______________________________________                                    

These Examples illustrate that excellent magnetic and physicalproperties can be obtained using the resins of this invention, whichresins have molecular weights considered suitable for magnetic recordingmedia formulations.

EXAMPLES 13-15

These Examples show the utilization of vinyl resins of the presentinvention, made using resins prepared in a direct polymerization, inmagnetic recording media.

Resins were prepared having the following compositions and physicalproperties, Example 13 being a control:

                  TABLE V                                                         ______________________________________                                                    Examples                                                                      13        14     15                                               ______________________________________                                        Composition                                                                   VCl           86          87     83                                           HPA           9           6      9                                            GMA           0.3         1.8    2.9                                          VAc           3.6         4.3    3.7                                          AA            1.1         0.9    1.4                                          Physical Properties                                                           Tg, °C.                                                                              77          77     75                                           Tensile Strength, psi                                                                       7500        6800   8200                                         Elongation %  23          20     32                                           Intrinsic Viscosity                                                                         0.51        0.51   0.58                                         ______________________________________                                    

No GMA was intentionally added in preparing the resin of Example 13. Theminor amount noted by analysis is believed due to contamination.

Magnetic recording media were prepared using the resins, and themagnetic properties and viscosity are set forth below:

                  TABLE VI                                                        ______________________________________                                                  Examples                                                            Property    13           14      15                                           ______________________________________                                        60° Gloss                                                                           64           20      58                                          SR          0.85         0.80    0.80                                         SFD         0.53         0.58    0.54                                         Hc          765          750     751                                          Viscosity, cps.                                                                           3000         4700    3000                                         ______________________________________                                    

These Examples demonstrate that magnetic recording media havingexcellent magnetic and physical properties may be obtained using resinsof the present invention made from a direct, one-step polymerization.While having acceptable magnetic and physical properties, the controlresin (Example 13) has significantly less thermal stability as seen inTable VII.

EXAMPLES 16-19

These Examples illustrate the increased thermal stability of the resinsof this invention.

Resin samples from prior Examples, together with comparative samples ofcommercially available vinyl chloride resins, were tested by placing apowder sample in a 5 cm. dish, 1 cm. deep, and then placing the samplesin a circulating air oven for 60 minutes. A visual rating was obtained(1--white, 2--pink, 3--tan, 4--brown, 5--black). The higher the number,the more extensive was the degradation.

Table VII sets forth the results:

                  TABLE VII                                                       ______________________________________                                        Example No. and       Visual                                                  Sample Designation    Rating                                                  ______________________________________                                        Ex. 16 -   non-phosphorylated                                                                           1                                                              intermediate of Ex. 10                                             Ex. 17 -   non-phosphorylated                                                                           1                                                              intermediate of Ex. 11                                             Ex. 18 -   resin of Ex. 15                                                                               1+                                                 Ex. 19 -   resin of Ex. 14                                                                               1+                                                 Control -  resin of Ex. 13                                                                              3                                                   Resin A                   3                                                   Resin B                   3                                                   ______________________________________                                    

As can be seen, the resins of the present invention may be prepared withvisually less thermal degradation than can prior vinyl chloridepolymers. A comparison of Examples 18 and 19 with the control (from Ex.13) illustrates that the thermal stability of the vinyl chloridecopolymers of this invention is markedly superior to that obtained whendirect polymerization is employed, but the resin does not include anadequate amount of an epoxy-containing vinyl monomer.

We claim:
 1. A vinyl chloride polymer suitable for use as a binder resinfor particulate material consisting essentially of:(a) vinyl chloride inan amount of about 70 to about 90 percent by weight; (b) hydroxyalkylacrylate in an amount to provide about 0.5 to about 3 percent by weighthydroxyl groups; (c) an epoxy containing vinyl monomer in an amount toprovide about 0.1 to about 1.5 percent by weight oxirane oxygen; (d)(i)acrylic acid, methacrylic acid, itaconic acid, fumaric acid or maleicacid; or (ii) a phosphorus compound providing a phosphorus ester moietycharacterized by the formula: ##STR3## wherein R is hydrogen, alkyl oralkenyl having from 1 to 20 carbon atoms, an alkyl acrylate ormethacrylate moiety having from 2 to 10 carbon atoms in the alkylsegment, a substituted or unsubstituted phenyl and mixtures thereof,component (i) when present, being in an amount sufficient to provideabout 0.2 to about 1.5 percent by weight carboxyl groups and component(ii) when present, being in an amount sufficient to provide about 0.03to about 1 percent by weight phosphorus.
 2. A vinyl chloride polymer asdefined in claim 1 consisting essentially of:(a) vinyl chloride in anamount of about 80 to about 90 percent by weight; (b) hydroxyalkylacrylate in an amount to provide about 0.5 to about 2.5 percent byweight hydroxyl groups; (c) an epoxy containing vinyl monomer in anamount to provide about 0.1 to about 1.5 percent by weight oxiraneoxygen and; (d) (i) acrylic acid, methacrylic acid, itaconic acid,fumaric acid or maleic acid in an amount to provide about 0.5 to about 1percent by weight carboxyl groups; or an amount of a phosphoruscompound, to provide about 0.03 to about 0.5 percent by weightphosphorus.
 3. A vinyl chloride polymer as defined in claim 1 consistingessentially of:(a) vinyl chloride in an amount of about 70 to about 90percent by weight; (b) hydroxyethyl acrylate or hydroxypropyl acrylatein an amount to provide about 0.5 to about 3 percent by weight hydroxylgroups; (c) an epoxy containing vinyl monomer in an amount to provideabout 0.1 to about 1.5 percent by weight oxirane oxygen; (d) maleic acidin an amount to provide about 0.2 to about 1.5 percent by weightcarboxyl groups.
 4. A vinyl chloride polymer as defined in claim 1consisting essentially of:(a) vinyl chloride in an amount of about 80 toabout 90 percent by weight; (b) hydroxyethyl acrylate or hydroxypropylacrylate in an amount to provide about 0.5 to about 2.5 percent byweight hydroxyl groups; (c) an epoxy containing vinyl monomer in anamount to provide about 0.1 to about 1.5 percent by weight oxiraneoxygen; (d) maleic acid in an amount to provide about 0.5 to about 1percent by weight carboxyl groups.
 5. A vinyl chloride polymer asdefined in claim 1 consisting essentially of:(a) vinyl chloride in anamount of about 70 to about 90 percent by weight; (b) hydroxyethylacrylate or hydroxypropyl acrylate in an amount to provide about 0.5 toabout 3 percent by weight hydroxyl groups; (c) an epoxy containing vinylmonomer in an amount to provide about 0.1 to about 1.5 percent by weightoxirane oxygen; (d) a phosphorous compound in an amount to provide about0.03 to about 1 percent by weight phosphorus.
 6. A vinyl chloridepolymer as defined in claim 1 consisting essentially of:(a) vinylchloride in an amount of about 80 to about 90 percent by weight; (b)hydroxyethyl acrylate or hydroxypropyl acrylate in an amount to provideabout 0.5 to about 2.5 percent by weight hydroxyl groups; (c) an epoxycontaining vinyl monomer in an amount to provide about 0.1 to about 1.5percent by weight oxirane oxygen; (d) a phosphorous compound in anamount to provide about 0.03 to about 0.5 percent by weight phosphorus.7. A vinyl chloride polymer as defined in claim 1 wherein the phosphoruscompound is phosphorus pentoxide.
 8. A vinyl chloride polymer as definedin claim 1 wherein the phosphorus compound is polyphosphoric acid.
 9. Amagnetic recording medium comprising a substrate and a magneticrecording layer thereon comprising magnetic particles and as a bindertherefor, the cured produce of the vinyl chloride polymer defined inclaim
 1. 10. A magnetic recording medium comprising a substrate and amagnetic recording layer thereon comprising magnetic particles and as abinder therefor, the cured product of the vinyl chloride polymer definedin claim
 5. 11. A magnetic recording medium comprising a substrate and amagnetic recording layer thereon comprising magnetic particles and asthe binder therefor, the cured product of the vinyl chloride polymerdefined in claim
 5. 12. The cured product of the polymer defined byclaim
 1. 13. The vinyl chloride polymer of claim 1 wherein component (b)is hydroxpypropyl acrylate.
 14. The vinyl chloride polymer of claim 1wherein component (b) is hydroxyethyl acrylate.
 15. The vinyl chloridepolymer of claim 1 wherein component (c) is glycidyl methacrylate. 16.The vinyl chloride polymer of claim 1 wherein component (c) is glycidylacrylate.
 17. The vinyl chloride polymer of claim 1 wherein component(c) is 4-vinylcyclohexene monoepoxide.